Method of coating metallic articles with vinyl resin dispersions



April 24, 1951 J. w. DONNELL ETA METHOD OF COATING L METALLIC ICLES WITHART VINYL RESIN DI RSIONS Filed June 1947 l5 3m. Q I 2 in. g ,l5 (in.

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' John W. Donnell 8 Kenneth Tater w W a 53 Patented Apr. 24, 1951 assertOFFiCE METHOD OF COATING METALLIC ARTICLES WITH VINYL RESIN John W.Donnell, East Lansing,

DISPERSIQNS Mich and Kenneth Tator, Sewickley, Pa., assignors toIndustrial Lining Engineers, corporation of Pennsylvania,

Application 'June 11, 1947, Serial No. 754,045

7 Claims.

This invention relates to articles of manufacture having corrosion-proofcoatings thereon and to the process for producing resinouscorrosion-proof coatings on metallic articles of manufacture;

I-Ieretofore, films of corrosion-proof materials have been applied tometals in many different ways, the commonest being tobuild up adesirable thickness'by applying successive layers of the corrosion-proofmaterial and heating such layers to remove solvents therefrom and toconvert the corrosion-proof materials to their final form. Such practiceis unsatisfactory as it is time consuming and the final product may havepoor adhesion between layers or porosity in the thin individual layers.

An object of this invention is to provide an adherent corrosion-proofcoating of a vinyl compound on metal articles of manufacture.

Another object of this invention is to provide for producing in a singleapplication a corrosion-proof coating of predetermined thickness between1% inch and inchof a vinyl compound.

; A further object of this invention is to provide for immersinga metalarticle in a supply of unheated viscous vinyl compound and solidifying alayer of predetermined thickness of the vinyl compound on the immersedmetal article without detrimentally affecting the remainder of thesupply;

A more specific object of this invention is to provide, in a process ofproducing corrosionprcof coatings on metal articles, for heating themetal article to a predetermined temperature and immersing the heatedarticle in a supply of unheated viscous solvent-free vinyl baseplastisol for a predetermined period of time to effect a solidificationof the plastisol adjacent the v heated article to produce an ofpredetermined thickness of the solidified vinyl compound thereon, thesolidified coating being adherent coating free of seams and flaws.

' Other objects of this invention will become apparent from thefollowing description when taken in conjunction wit the accompanyingdrawing, in which:

Figure 1 is a schematic illustration of apparatus utilized in practicingthe teachings of this invention,

Fig. 2 is a graph, the curves of which illustrate the relationshipbetween the thickness of the coatings produced at different temperaturesin practicing this invention and the eifect of the relationship of thevolume to the surface area of the article on such coatings, and

rm, Sewicklcy, Pa, a

3 is a graph, the curves of which illustrate the effect of time on thethickness of the coatings produced at different temperatures for a givenarticle of constant volume to surface area ratio.

In practicing this invention the articles to be coated are first cleanedas by sand blastingto remove scale, rust and the like from the surfacethereof. The sand blasting also functions to etch the surface to therebyrender it more receptive for receiving and retaining a coating thereon.After the surfaces of the article are thoroughly cleaned, a thin coatingof a suitable primer is applied thereto as by dipping the article in asupply of the primer or brushing the primer thereon.

Different primers are well known in the art and can be successfullyemployed. For example, the primer may be a chlorinated rubber solution,or a solution of either vinyl resins or'vulcanized, natural or syntheticrubberor a coinbination thereof. In a preferred form for cooperatingwith the coating to be applied as described hereinaftenthe primer is asolution of vulcanizable synthetic rubber of the acrylonitrile type andvinyl resin.

The primer applied to the cleaned surface of the article bonds with theetched surface thereof being reacted when subjected to heat to provide athin, solid coating. For example, the coating of the primer lastreferred to can be completely reacted by heating the primer coatedarticle at a temperature of about 300F. for about 2 hours or may be onlypartially reacted by heating it for a shorter period of time to driveoff the solvents thereof, the reaction being completed during theapplication of a corrosion-proof coating to be next described. v

The corrosion-proof coating of this invention is formed from a syntheticresinous thermoplastic composition such as vinyl plastisol. The vinylplastisol is a dispersion of high molecular weight .resins, essentiallyvinyl chloride, in a suit thereto, there is a change in phase in thatthe as carried by the conveyor Referring to Figure 1, there is adiagrammatic illustration of apparatus employed in applying theplastisol to the articles which are provided with the primer coating. Asillustrated, the apparatus generally comprises a furnace l0, and acontinuous conveyor belt or chain 14 having hooks l6 thereon in spacedrelation for holding the articles 18 which are to be coated. The furnaceI is of sufficient size and length so that a number of the articles l8will be contained therein at any given time.

The conveyor belt M is disposed for intermittent operation to be solowered as it leaves the furnace I0 that an article 18 carried by thebelt 14 may be dipped and held immovable within the supply l2 of vinylplastisol as will be de scribed hereinafter. The articles [8 are sospaced belt 44 that as one supply I2, the next held in the furnacearticle is immersed in the and succeeding articles are In accordancewith this invention, the articles l8 having the primer coating (notshown) thereon are carried into the furnace i0 where they are subjected.to sufficient heat to develop heat in the articles of between 225 F. and350 F. depending on the size and shape of the articles H]. The relationof the volume to the surface area of the article being coated and thetemperature to which the article is heated determines the thickness ofthe coating formed thereon for any given time of immersion.

During the heating of the articles in the furnace II] the primer coatingis at least more completely reacted to give a solid film of the primer.When the required temperature is developed in the article 18, the beltH3 is intermittently actuated to advance one of the heated articles 18directly from the furnace I0 into the supply 12 of the unheated viscousvinyl plastisol where the heated article I8 is held immovable for aperiod of time of from minute to 7 minutes depending upon thetemperature of the article and the thickness of the coating to beproduced.

When the heated article 18 is dipped into the vinyl plastisol andmaintained immovable therein, it is found that the heat of the metaleffects a more complete reaction of the primer if not heretoforecompletely reacted, and simultaneously therewith causes the adjacentlayer of the vinyl plastisol to convert to the solid stage in adheringrelation to the heated article. The conversion is outward from thesurface of the article l8 so that by controlling the time of immersionthe thickness of the adhering layer or coating 20 of converted plastisolcan be controlled. During the immersion, it is thought that the heat ofthe metal causes the plasticizer to go into the vinyl resin to changeits phase and that thereafter the heat causes a coalescence of thediscrete particles of resin by natural fusion process.

By maintaining the article immovable in the supply I2 of vinylplastisol, smooth, uniform coatings 20 are produced which are free fromany detectable swirls, voids, overlaps or the like.

After the predetermined layer 29 of converted plastisol is formed on thearticle 18, the conveyor belt 14 is actuated to remove the coatedarticle from the supply l2 and to advance another one of the heatedarticles l8 forward from the furnace l0 into the supply [2. As thecoated article is removed from the supply 12, any excess 4 ofunconverted plastisol is readily removed from the coated article bywiping such article leaving a smooth seamless and adherent coating 20 onthe article.

Referring to Figure 2, the curves therein illustrate the efiect of thetemperature of the metal articles on the thickness of the coating 20 ofthe converted plastisol for different volume'to surface area ratios asfound in working with many different shaped and sized articles with aconstant dip or immersion time of 2 minutes. The curves of Fig. 2 areself-explanatory and clearly show that as the volume to area ratio (V/A)increases, the heat content of the article so increases that for a giventime of immersion the thickness of the coating formed on the articleincreases. Thus for any given metallic article having a predeterminedvolume to area ratio the thickness of the coating formed can be closelycontrolled by controlling the temperature developed in the article.

Referring to Fig. 3 of the drawing, the effect of the temperature of theheated article on the thickness of the coating formed on an articlehaving a predetermined volume to area ratio of .1875 is illustrated fordifferent lengths of time of immersion as indicated. Thus by developinga temperature in the article of 300 F. and dipping the heated article inthe vinyl plastisol for 1 minute a coating having a thickness of .14inch can be produced whereas if the time is extended to 6 minutes, acoating having a thickness of .20 inch is obtained. Little, if any,advantage is obtained by extending the dipping time beyond this periodas the heat content is apparently dissipated or is so low at this pointthat it fails to convert additional plastisol to a solid.

On the other hand, if a thicker coating is required, then the articleshould be initially heated in the furnace to develop a highertemperature therein. Thus when a temperature of 350 F. is developed inthe primer coated article which is then immersed and maintainedimmovable in the vinyl plastisol for about 5 minutes, it is possible toproduce a coating of .25 inch thickness on the article.

In practice, it is desired-to maintain the heat of the article at notless than 225 F., as temperatures below that temperature will producecoatings of insufficient thickness. However, it is also necessary tomaintain the temperature of the heated articles at not more than 350 F.as the coatings formed at higher temperatures have poor adhesion andcontain voids resulting in uneven coatings. Preferably the heatingtemperature should be-maintained between 275 F. and 325 F. for bestresults.

After the adhering coating is thus formed on the article, the coatedarticle is subjected to a further heat treatment or baking at atemperature between 350 F. and 375 F. for a period of time ranging from4 min. to 4 hrs. depending upon the thickness of the coating and thearticle coated to effect the fusing of the solids of the film or coatingand to impart strength to the resulting resilient coating. It has alsobeen found that this latter heat treatment is also effective forcompleting the reaction of the primer if such reaction had notheretofore been completed.

In ourcopending application Serial No. 754,044, filed simultaneouslyherewith, there is a disclosure of the process of producing the resinouscorrosion-proof coatings on metallic articles of large surface area. Asdisclosed therein the articles, such as plate stock, vessels and othermetal covered thereby,

articles of manufacturewhich have largesurface areas have. the surfaceswhich are to be coated cleaned as by sand blasting to remove scale,

rust and the like, after which, a primer of the type disclosed herein isapplied as by spraying or brushing. The large surfaces are preferablydesignated into smaller areas and marked with a heat responsivetemperature indicating means, such as a temperature responsive crayonhaving a definite range of melting temperature. Heat is then applied asby means of a direct flame to one of the smaller designated areas untilthe temperature responsive crayon marks indicate that the metal of thedesignated area is heated to a temperature in the range of 275 F. and'350'F., which heating effects the reaction of the primer to arelatively solid layer. The-vinyl plastisol is then applied to theheated area, the heat of the metal converting the plastisol to the solidstage in adhering relation to the heated article. The adjacent smallareas are similarly treated until the entire surface which-is to becoated is given a uniform coating, the adjacent areas being coated witha layer of the solidified plastisolwhich is free from detectable joints,marks or flaws. A further heat treatment of the coated article at atemperature between 350. F. and 375 F. is found to effect the fusing ofthe solids of the vinyl coating and to impart strength to the resultingresilient coating. This latter heat treatment also completes thereaction of the primer if not completed heretofore.

Corrosion-proof coatings ranging from to /2 inch can be readily formedon articles by following the teachings of this invention. Such coatingsare also abrasion resistant, resilient and strong being very adherent tothe surface of the article.

We claim as our invention:

1. The process of producing a corrosion-proof coating on a surfacefacture comprising, in. combination, applying a primer consisting of asolution of at least one substance selected from the group consisting ofrubber and vinyl resins to the surface of the article to be coated,heating the article to develop a temperature therein between 275 F. and355 F., immersingthe heated article while the article retains atemperature between 275 F. and 350 F. in a supply of unheated viscouscompound comprising a solvent-free dispersion of vinyl chloride-acetatecopolymer in a liquid plasticizer for a period of time of between minuteand 7 minutes, the heat in the phase of the viscous compound closelyadjacent to the metal to solidify a layer of the compound in adheringrelation to the primer and removing the coated article from the supply,and thereafter baking the coated article at a temperature between 350 F.and 375 F. to fuse the solids of the solidified layer,

2. The process for producing a corrosion-proof coating on the surface ofa metallic article of manufacture comprising, in combination, applying apolymerizable primer consisting of a solution of at least one substanceselected from the group consisting of rubber and vinyl resins to thesurface of the article to be coated, heating the article to' develop atemperature therein between 225 F. and 350 F. and at least partiallypolymerize the primer, immersing the primer coated surface of the heatedarticle while the article retains a temperature between 225 F. and 350F. ina supply of unheated viscous solventof a metallic article of manuF. and 350 of the metal effecting a change t 6 free vinyl compoundconsisting of a dispersion of vinyl chloride-acetate copolymer having96% vinyl chloride in a plasticizer therefor, maintaining the heatedarticle stationary in the unheated vinyl compound for a period of timeof between minute and 7 minutes during which the heat of the metaleffects the completion of the polymerization of the primer andsimultaneously therewith effects a change in the phase of the vinylcompound adjacent the primer to solidify alayer of the compound inadhering relation to the primer and metal covered thereby, removing thecoated article from the supply, thereafter removing unsolidified vinylcompound carried on the surface of the solidified layer when the coatedarticle is removed from the supply to produce a smooth, seamless,tightly adhering, corrosionproof coating having a thickness of between1% inch and inch on the metal article, and thereafter baking the coatedarticle at a temperature between 350 F. and 375 F. to fuse the solids ofthe solidified layer.

3. The process for producing a corrosion-proof coating on the surface ofa metallic article of manufacture comprising, in combination, applying aprimer consisting of a solution of at least one substance selected fromthe group consisting of rubber and vinyl resins to the surface of thearticle to be coated, heating the article to develop a predeterminedtemperature between 225 F. therein, immersing the primer coated surfaceof theheated article while the article retains a temperature between 225F. and 350 F, in a supply of viscous solvent-free vinyl compoundconsisting of a dispersion of vinyl chloride-acetate copolymer havingabout 96% vinyl chloride in a plasticizer therefor for a period of timeof between minute and 7 minutes to eifect a change in phase of the vinylcompound adjacent the heated article to solidify a predetermined layerbetween inch and inch thick of the vinyl compound in adhering relationto the primer and metal covered thereby, removing the coated articlefrom the sup ly, and thereafter heating the coated article at atemperature between 350 F. and 375 F. to fuse the solidsof thesolidified layer. 7

' 4. The process for producing a corrosion-proof coating on the surfaceof a metallic article of manufacture comprising, in combination,applying a primerconsisting of a solution of vulcanizable syntheticrubber of the acrylo-nitrile type and vinyl resin to the surface of thearticle to be coated, heating the article to develop a temperaturetherein between 225 F. and 350 F. and

at least partially react the primer, immersing the primer coated surfaceof the heated article while the article retains a temperature between225 F. and 350 F. in a supply of unheated viscous vinyl compoundconsisting of a dispersion of vinyl chloride-acetate copolymer having96% vinyl chloride in a plasticizer therefor for a time of betweenminute and 7 minutes, the heat of the metal completing the reaction ofthe primer and simultaneously therewith effecting a change in the phaseof the vinyl compound adjacent the primer to solidify a layer of thecompound in adhering relation adjacent the primer and metal coveredthereby, removing the coated article from the supply, and thereafterbaking the coated article at a temperature between 350 F. and 375 F. tofuse the solids of the solidified layer.

5. The process for producing a corrosion-proof coating on the surface ofa metallic article of manufacture comprising, in combination, applying aprimer consisting of a solution of vulcanizable synthetic rubber of theacrylo-nitrile type and vinyl resin to the surface of the article to becoated, heating the article to develop a temperature therein between 225F. and 350 F. and at least partially react the primer, immersing theprimer coated surface of the heated article while the article retains atemperature between 225 F. and 350 F. in a supply of unheated viscoussolvent-free vinyl compound consisting of a dispersion of vinylchloride-acetate copolymer havin 96% vinyl chloride in a, plasticizertherefor, maintaining the heated article stationary in the unheatedvinyl compound for a period of time of between A; minute and '7 minutesduring which the heat of the metal effects the completion of thereaction of the primer and simultaneously therewith effects a change inthe phase of the vinyl compound adjacent the primer to solidify a layerof the compound having a thickness of between inch and /2 inch inadhering relation to the primer and metal covered thereby, removing thecoated article from the supply, and thereafter baking the coated articleat a temperature between 350 F. and 375 F. to fuse the solids of thesolidified layer.

v 6. The process of producing a corrosion-proof coating on the surfaceof a metallic article of manufacture comprising, in combination,applying a primer consisting of a solution of vulcanizable syntheticrubber of the acrylo-nitrile type and vinyl resin to the surface of thearticle to be coated, heating the article to develop a temperaturetherein between 225 F. and 350 F. and at least partially react theprimer, immersing the primer coated surface of the heated article whilethe article retains a temperature between 225 F and 350 F. in a supplyof unheated viscous solvent-free vinyl compound consisting of 50 partsby weight of vinyl chloride-acetate copolymer having 96% vinyl chlorideand 50 parts by weight of a plasticizer therefor for a time of between Aminute and '7 minutes, the heat of the metal completing the reaction ofthe primer and simultaneously therewith effecting a change in the phaseof the vinyl compound adjacent the primer to solidify a layer of thecompound in adhering relation adjacent the primer and metal coveredthereby, removing the coated article from the supply, and thereafterbaking the coated article at a temperature between 350 F. and 375 F. tofuse the solids of the solidified layer.

'7. The process of producing a corrosion-proof coating on a surface of ametallic article of manufacture, comprising, in combination, applying aprimer consisting of a solution of at least one substance selectedfrom'the group consisting of rubber and vinyl resins to the surface areaof the article to be coated, heating a portion of the area to be coatedto develop a temperature therein between 225 F. and 350 F., applying 'alayer of unheated viscous compound comprising a solvent-free dispersionof vinyl chloride-acetate copolymer in a liquid plasticizer to theheated portion of the area to be coated while the heated portion retainsa temperature between 225 F. and 350 F., the heat of the metal effectinga change in the phase of the viscous compound to solidify the layer ofthe compound from the metal outwardly in adhering relation to the primerand metal covered thereby, and thereafter baking the coated article at atemperature between 350 F. and 375 F. to fuse the solids of thesolidified layer.

JOHN W. DONNELL. KENNETH TATOR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Powell, Vinylite ResinDispersions, Off. Digest N0. 263, D80. 1946, pgs. 696-702.

1. THE PROCESS OF PRODUCING A CORROSION-PROOF COATING ON A SURFACE OF A METALLIC ARTICLE OF MANUFACTURE COMPRISING, IN COMBINATION, APPLYING A PRIMER CONSISTING OF A SOLUTION OF AT LEAST ONE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF RUBBER AND VINYL RESINS TO THE SURFACE OF THE ARTICLE TO BE COATED, HEATING THE ARTICLE TO DEVELOP A TEMPERATURE THEREIN BETWEEN 275* F. AND 350* F., IMMERSING THE HEATED ARTICLE WHILE THE ARTICLE RETAINS A TEMPERATURE BETWEEN 275* F. AND 350* F. IN A SUPPLY OF UNHEATED VISCOUS COMPOUND COMPRISING A SOLVENT-FREE DISPERSION OF VINYL CHLORIDE-ACETATE COPOLYMER IN A LIQUID PLASTICIZER FOR A PERIOD OF TIME OF BETWEEN 3/4 MINUTE AND 7 MINUTES, THE HEAT OF THE METAL EFFECTING A CHANGE IN THE PHASE OF THE VISCOUS COMPOUND CLOSELY ADJACENT TO THE METAL TO SOLIDIFY A LAYER OF THE COMPOUND IN ADHERING RELATION TO THE PRIMER AND METAL COVERED THEREBY, REMOVING THE COATED ARTICLE FROM THE SUPPLY, AND THEREAFTER BAKING THE COATED ARTICLE AT A TEMPERATURE BETWEEN 350* F. AND 375* F. TO FUSE THE SOLIDS OF THE SOLIDIFIED LAYER. 